Receptor coating for image transfer

ABSTRACT

A WATER BASED RECEPTOR COATING FOR IMAGE RECEIVING SUBSTRATES FORMED OF THE DRIED RESIDUE OF A FINELY DIVIDED HYDROCARBON WAX EMULSION HAVING APYROGENIC SILICA MATRIX FORMING AGENT AND A PIGMENTED FILLER DISPERSED THEREIN AND IN WHICH THE SIZE OF THE WAX PARTICLES DOES NOT EXCEED 25 MICRONS AND THE PARTICLE SIZE OF THE MATRIX FORMING AGENT DOES NOT EXCEED .05 MICRON.

United States Patent 01 3,658,998 Patented Apr. 25, 1972 hce 3,658,998 RECEPTOR COATING FOR IMAGE TRANSFER Gerry H. Ehrhardt, West Des Moines, and Timothy G. Abernathy, Clive, Iowa, assignors to Pacific Industries, Inc., San Francisco, Calif. No Drawing. Filed Aug. 31, 1967, Ser. No. 664,615 Int. Cl. C09d 3/44 US. Cl. 117-168 4 Claims ABSTRACT OF THE DISCLOSURE A water based receptor coating for image receiving substrates formed of the dried residue of a finely divided hydrocarbon wax emulsion having apyrogenic silica matrix forming agent and a pigmented filler dispersed therein and in which the size of the wax particles does not exceed 25 microns and the particle size of the matrix forming agent does not exceed .05 micron.

This invention relates to an improved coating for enhancing the reception of images from auxiliary transfer media.

The rapidly expanding use of data processing and automated reproduction equipment has created a need for transfer media capable of producing greater numbers of higher quality copies per impression than that obtainable from conventional transfer media. In attempted satisfaction of such need, one of the conventional techniques employed is the use of specially constituted image receiving surfaces having a preferential, and often selective, affinity for a particularly constituted transfer coating. Eiforts to date in this field however have not been characterized with marked success and have essentially failed to bridge the wide gap now extant between what is desired and what is actually available.

Some of the relatively recent eiforts in this area are exemplified by the recently issued U.S. Pats. Nos. 3,169,880 and 3,186,862. Both of these patents disclose formulations for specially constituted image receiving surfaces having an assertedly high degree of selectivity and comprising, in the first case, a mixture of certain resins and soluble plasticizers therefor and in the latter case a mixture of ozocerite and paraffin waxes and polyisobutylene. These comparatively late specially constituted image receiving surfaces, however, are essentially possessed of the same characteristic deficiencies that have been long and generally attendant such specialized selective image receptor surfaces, at least when the same are constituted within the dictates of economic reality. Among these characteristic deficiencies are the required utilization of a relatively opaque and dense carrier substrate to minimize penetration of the carrier by the essentially resinous and waxy receptor coatings with its undesired and attendant degree of transparency. More importantly, however, the inherent nature of both of these coatings is characteristically in the form of a continuous, impervious film which, apart from the selective ,or preferential reception of a particularized compatible transfer coating, effectively minimizes, if not prevents, ink and oil penetration in other applications. This latter, of course, detrimentally affects the ability of the coated receptor sheet to be printed and to receive handwritten images thereon as by the use of fountain pens, ballpointpens and, in some instances, even pencil. In fact, water inks are actually repelled by such coatings. Experience with such continuous and impervious type receptor coatings has also demonstrated a characteristic inability of glues to penetrate and form a bond with either the coating or underlying substrate as well as the tendency of such coatings of the wax base variety to come off and adhere, in whole or in part, on printing press plates and the like with the attendant need for increased maintenance in conjunction therewith.

These characteristic deficiencies normally attendant to conventionally formulated receptor coatings have not only effectively impeded their utilization in the obtaining of increased numbers of copies in various types of printing apparatus but have also been so marked as to generally minimize their utilization even where lesser numbers but yet higher quality of copies are required.

This invention may be briefly described as an improved image receiving coating material comprising the dried residue of a water based dispersion of a finely divided wax emulsion, a highly dispersible matrix forming agent of a particle size markedly less than that of the wax emulsion component and a pigmented filler, disposed as an essentially discontinuous or pervious film on the surface of a basal substrate.

Among the advantages of the subject invention is the production of an improved receptor sheet of essentially non-selective or non-preferential character but with generally enhanced receptor affinity for transfer coatings employed in mechanical type carbonless copy papers and which is substantially free from most, if not all, of the characteristic deficiencies of the receptor sheets of the art. Still another advantage is the enhancement of the appearance and characteristics of the carrier sheet both as to capacity and printability. More specifically the receptor coating formulations herein disclosed serve, in addition to satisfying the need for increased numbers of copies of improved image receptor quality, to form a pervious coating thereon, to act as a filler to enhance the dimensional uniformity and opacity of the substrate as well as its tensile strength and to provide, as well, a sheet that Will readily accept direct image application from ballpoint and fountain pens, from pencils and the like and from water based inks.

'The primary object of this invention is the provision of an improved coating formulation for image receiving substrates and the improved image receptor sheet resulting therefrom.

Another object of this invention is the provision of an improved image receptor coating formulation that enhances the appearance and characteristics of the carrier substrate.

Other objects and advantages of the invention will become apparent to those skilled in this art from the following portions of this specification which describe, in more detail, the principles of this invention and the presently preferred embodiments thereof incorporating such principles.

The image receptor coating material formed in accordance with the principles of this invention broadly comprises the dried residue of a water based dispersion of a finely divided wax emulsion, a highly dispersible matrix forming agent, and a pigmented filler. Such water based dispersions constituted as hereinafter described are readily applicable to a carrier substrate by any of the conventional methods, such as by roll coating, air knife, doctor blade or spraying, and, after drying, apparently form a pervious or discontinuous film on the substrate of such character as to produce the markedly advantageous results outlined above.

The water based finely divided wax emulsion component is desirably formed of a mixture of waxes and constitutes from about 50 to 80% (on a dry weight basis) of the dry effective coating constituents and with the preferred range thereof falling between 60 to The particular waxes employed and the proportions thereof utilized in forming this component are largely determined by the nature of the image producing material and by the definition of the image to be transferred together with the pressure available for effecting image transfer. Suitably saidwax'emulsion component is formed of a base hydrocarbon wax, one or more emulsifiable additives and one or more emulsifying agents, with the particle size of the solid emulsion constituents being critically held below about 20 to 25 microns and preferably being held within the to micron particle size range. The base hydrocarbon wax suitably comprises hard and soft microcrystalline waxes and paraflin wax. The emulsifiable additives suitably comprise vegetable wax, mineral wax, oxidized microcrystalline wax or oxidized polyethylene. The preferred emulsifying agents comprise oleic acid and morpholine although many of the well known emulsifying agents such as triethanolamine, stearic acid, diisopropanolamine, as well as commercial surfactants such as Span (sorbitan mono laurate) and Tween 20 (polyoxyethylene (20) sorbitan monolaurate), were tested and found to give similar results. If desired, a small amount of wax modifiers may be used to soften the hard microcrystalline waxes and provide somewhat softer characteristics in the resultant coating. Basically, however, the hardness of the coating will be determined by the amount and type of the base hydrocarhon 'waxes employed.

The highly dispersable matrix forming agent preferably comprises pyrogenic silica having a critical particle size of not greater than about .05 micron preferably having an cfiective particle size less than .02 micron. Amounts thereof falling within about 2 to 10% (on a dry weight basis) provide generally satisfactory results although amounts in the range of 4 to 7% are preferred.

The pigmented filler serves to add opacity and/ or color to the coating residue and suitable materials include coating clays, calcium carbonate, titanium dioxide and lithopone. If color other than white is desired small amounts of dyes are added. The amount of the pigmented filler is not particularly critical and is largely determined by the quality and porosity of the substrate that is employed. Amounts ranging from zero, where a high quality substrate is employed, up to 50%, where a poor quality highly porous substrate is employed have proved to be satisfactory. In general, however, the preferred range will fall within about 15 to Intermixture of the above described constituents is effected by first forming a slurry or dispersion of the pigmented filler and the matrix forming agent in water and then slowly and with continual stirring adding the previously prepared wax emulsion thereto. After uniform mixture has been effected the coating material is applied, as heretofore noted, by any of the conventional coating methods to a substrate and dried, in situ, thereon.

The following constitute, by way of illustrative example, some representative formulations for image receptor coatings (on a dry weight basis) incorporating the principles of this invention.

The following formulation has provided a coating with good image receiving characteristics and opacity and of a character that prints exceedingly Well.

FORMULATION A Wax emulsion component:

A somewhat less expensive formulation having good ""printabilityand image receiving characteristics but with lesser opacity is as follows: FORMULATION B Wax emulsion component: Percent Oxidized polyethylene 11.3% Hard microcrystalline wax 28.6%

Soft microcrystalline wax 9.2% 64.1 Oleic acid 7.4% Triethanolamine 9.4%

Matrix forming agent:

Pyrogenic silica 5.8

Pigmented filler:

Coating clay 14.0%} Titanium dioxide 8.0%

"Wax..modifiers Wax emulsion component: Percent Matrix forming agent:

Oxidized microcrystalline wax 14.0% Hard microcrystalline Wax 45.0% 66.0 -Oleic acid ....7.0%

Pyrogenic silica 4.0 Pigmented filler:

Titanium dioxide 30.0

While the basic physical and operational characteristics of the image receptor film disclosed herein are not fully understood at the present time, it is believed that the pyrogenic silica apparently serves to form a reticulated matrix that separates or perhaps partially or entirely encapsulates the individual wax constituent particles and thus forms a discontinuous or pervious film in which the shells or reticulated structure thereof is fractured upon pressure application to thereby allow the wax particles to act as image receiving elements. The matrix forming agent apparently functions to prevent wax migration, even under heat, to present a non-waxy surface and to selectively render the wax re-accessible in response to pressure application. Experiments to date have indicated that omission of the matrix forming agent results in the formation of continuous and essentially impervious films with the characteristic disadvantages thereof pointed out at an earlier point in this specification. Experiments to date have also shown that, for the formulations above set forth, the temperature can be raised well above the melting point or film forming temperatures of either of the wax materials employed Without any continuous film formation.

Having thus described our invention, we claim:

1. On a supporting basal substrate, an image receptor pervious coating formed of the dried residue of a water based dispersion comprising 50 to of a wax emulsion constituent consisting essentially of discrete particles of a base hydrocarbon wax having a particle size not greater than 25 microns, an emulsifiable additive separate from said base hydrocarbon wax and an emulsifying agent,

2 to 10% of a highly dispersible pyrogenic silica matrix forming agent having a particle size not greater than about .05 micron and not more than 50% of a pigmented filler.

2. The receptor coating as set forth in claim 1 wherein said base hydrocarbon wax is selected from the group consisting of microcrystalline and paraflin waxes and said emulsifiable additive is selected from the group consisting of vegetable wax, mineral wax, oxidized microcrystalline wax and oxidized polyethylene.

3. The receptor coating as set forth in claim 1 wherein said matrix forming agent is pyrogenic silica having a particle size of less than .05 micron.

4. The receptor coating as set forth in claim 2 wherein said wax in said wax emulsion has a particle size of less than 10 microns, and said matrix forming agent is pyrogenic silica having a particle size of less than .02 micron.

References Cited UNITED STATES PATENTS 2,597,872 4/1952 Iler 117169 A 6 Klimkowski 106-272 Steinhardt 106-272 Johnson 161--1l6 Renter 11783 FOREIGN PATENTS Canada 106272 WILLIAM D. MARTIN, Primary Examiner US. Cl. X.R. 

